(1) Field of the Invention
This invention relates to a substrate treating system for transporting, to and from a substrate treating apparatus, pods containing semiconductor wafers, substrates for liquid crystal displays, substrates for plasma displays, substrates for organic EL devices, substrates for FEDs (Field Emission Displays), substrates for optical displays, substrates for magnetic disks, substrates for magnetic optical disks, substrates for photomasks, or substrates for solar cells (hereinafter called simply substrates).
(2) Description of the Related Art
Conventionally, a substrate treating system of this type includes a substrate treating apparatus having a substrate treating unit, a pod storage and transport unit, and a load port, and a carrier transport system for transporting pods upon instructions of a host computer which performs overall control of the treating system.
The substrate treating unit carries out various types of treatment for substrates. The pod storage and transport unit is juxtaposed to the substrate treating unit for storing and transporting FOUPs (Front Opening Unified Pods) containing the substrates. The load port is juxtaposed to the pod storage and transport unit for receiving the FOUPs. The carrier transport system is an automated material handling system (AMHS) having automatic guided vehicles (AGV), or an overhead hoist transfer (OHT), which transfers the FOUPs to and from the load port. The host computer carries out controls relating to transportation of the FOUPs through communication with the substrate treating apparatus and the carrier transport system
It takes time for the carrier transport system to transport the FOUPs to the substrate treating apparatus. Therefore, where the substrate treating apparatus has the pod storage and transport unit, it is required, after a FOUP is loaded into the load port, to take the FOUP from the load port into the pod storage and transport unit as soon as possible, to vacate the load port for receiving a next FOUP. In order to meet such a requirement, a proposal has been made to provide a movable buffer as a temporary passing place for pods adjacent the load port. See Japanese Patent National Publication No. 2008-508731, for example.
This apparatus, when a FOUP is placed on the load port, operates the movable buffer to slide the FOUP side-ways for temporary displacement from the load port, thereby making the load port available for a next transporting action.
However, the conventional example with such construction has the following drawback.
Although the conventional apparatus has the mechanism for temporarily displacing FOUPs from the load port, an inconvenience occurs when, for example, two OHTs of the carrier transport system consecutively carry FOUPs to the same load port. Since the loading intervals are short, there occurs a problem that, before the FOUP loaded by one OHT into the load port is displaced therefrom, the other OHT may attempt and fail to load the other FOUP into the load port. Immediately upon such loading failure, the load port reports “loading disapproval” for that OHT to the carrier transport system. Then, the OHT will move past the load port and along a circulating track of the carrier transport system, and will thereafter make a loading attempt again. The same problem may arise in unloading. Therefore, moving along the circulating track is time-consuming, which poses a problem that the resources of the carrier transport system cannot be used effectively.